The MuCell Injection Molding Process: A Strategic Cost Savings Technology for Electronic Connectors

Transcription

1 The MuCell Injection Molding Process: A Strategic Cost Savings Technology for Electronic Connectors September 18-19, 23 L. J. Hyde and L. A. Kishbaugh Trexel, Inc. International Institute of Connector and Interconnection Technology, Inc. (IICIT) Annual Symposium ABSTRACT The MuCell injection molding process is being applied by the world s leading electronic connector manufacturers as a core plastics manufacturing technology to obtain (1) faster product development capability, (2) operating and capital cost savings and (3) productivity improvements. The MuCell injection molding process results in electronic connector components that have less residual stress, superior conformance to mold dimensions, and improved dimensional stability at extreme operating and soldering temperatures compared to conventionally molded parts. The MuCell microcellular foam injection molding process uses supercritical fluids (SCF) of inert gases, (nitrogen or carbon dioxide) to create evenly distributed and uniformly sized microscopic cells throughout a polymer. The MuCell process enhances thin-wall connector design, improves processing efficiency, and reduces product costs. Driven by compelling cost savings opportunities, a transition from conventional molding to MuCell microcellular foam processing is occurring within an extensive range of connection systems including wiring harness connectors, electronic control module headers, IC sockets including DIMM, DDR DIMM, and RIMM, fine pitch connectors, board level connectors, and PCMCIA connectors, and DIN connectors. The MuCell process has been deployed worldwide across an extensive range of automotive, business machinery, and industrial markets as a strategic cost savings technology. INTRODUCTION MuCell is a process and equipment technology for thermoplastic injection molded components that results in an average cost reduction of 12% to 2% compared to conventional molding of electronic connector parts. MuCell is a microcellular foam injection molding process that lowers the fundamental cost structure of injection molded connector components through 4 main sources of economic benefit: 1. The ability to mold stress-free thermoplastic parts with repeatable and predictable dimensions; 2. Reduced operating costs through cycle times reductions averaging 2% to 3%, reduced scrap rates, and lower energy consumption; 3. Capital cost avoidance through the procurement of smaller machines, fewer machines, and fewer molds; 4. Reduced material costs through lower cost material substitution and component density reduction of 4% to 12%. Using engineering thermoplastics such as PBT, Nylon 66, and to High Temperature Nylon (HTN), MuCell electronic connector components are being developed and commercialized in North America, Europe, and Asia for competitive and financial advantages derived from these strategic MuCell benefits: Cycle Time Reduction The MuCell process reduces cycle time by an average of 2% to 3% compared to conventional molding. This productivity benefit has tremendous economic significance to connector manufacturers from the standpoint of reduced operating costs, freed production capacity, and capital cost avoidance. Faster Product Release Part quality is achieved faster with the MuCell process through superior dimensional conformance to the mold and the elimination of residual stress. More consistent and predictable MuCell part dimensions compared to conventional molding lead to faster mold development, fewer tooling iterations, and ultimately the ability to commercialize connector products faster with less of a struggle to meet final print dimensions. Lower Cost Material Substitution With the trend toward smaller electronic connection designs, melt viscosity and

2 pressure reductions which takes place during MuCell processing result in a wider processing window to achieve complete filling of thin wall sections and flexible members without pressure induced stress. MuCell thereby expands the selection window of the least expensive material that is functionally suited for a given the application. An example is the replacement of conventionally molded liquid crystal polymers (LCP) with MuCell-molded high temperature nylons (HTN), with HTNs benefiting from improved flow and thermal stability using the MuCell process. MUCELL PROCESS FUNDAMENTALS The MuCell process begins by converting the inert gas, nitrogen or carbon dioxide, into a supercritical fluid, or SCF, for precise dosing capability. The SCF is injected into the barrel during screw recovery by the SCF interface kit that is mounted to the barrel. Consumer Electronics provides improved filling of thick wall sections located at the end of thin flow paths. In conventional molding, optimum part design includes gating such that thinner wall sections are at the end of fill and this gating location makes it difficult to completely pack out common electronic connector part geometries such as thin flexible members. The cell growth that occurs with the MuCell process allows complete filling of these thicker features providing a part with much sharper detail. MUCELL HARDWARE MuCell Modular Upgrade (MMU) The recently introduced MuCell Modular Upgrade (MMU) represents a significant advance for MuCell technology as A specially designed MuCell screw with a 22/1 L/D disperses the SCF into the polymer melt creating a single-phase solution. The SCF acts as a temporary polymer plasticizer, reducing the viscosity of the resin up to 3%. This provides the inherent benefit of improved filling of thin-wall sections and flexible members. During filling and cooling, microscopic cell growth takes place within the cavity, creating all of the internal pressure needed to completely fill the part. Thus pack and hold, a contributor to cycle time and major source of molded-in part stress in conventional molding, is eliminated with the process. Peak cavity pressure is reduced by up to 8%. Cooling time is often shortened due to reduced mass and lower mold and melt temperatures. Cycle time reductions averaging 2% to 3% translate into capital cost avoidance and freed machine capacity. A uniform closed-cell, microscopic cell structure is created throughout the part with a solid skin. Stress induced warpage is eliminated and sink marks are eliminated without a chemical change to the polymer. The elimination of the hold phase results in a significantly lower peak clamp tonnage requirement. This allows machine size reduction by up to 5% using MuCell processing and reduced operating costs through the use of the lower corresponding hourly machine rate. Replacing the pack and hold phase of the conventional molding process with cell growth of the MuCell process FIGURE 1 The MuCell Process Provides 3 Economic Benefits in Connectors/Sockets for Computer, Communication, & nearly any injection molding machine can be easily converted to a MuCell injection molding machine. The MMU allows direct replacement of current screws and barrels without complex and costly mechanical adaptations. FIGURE 2 MuCell Injection Module for MuCell Modular Upgrade The MuCell process is also available on new electric and hydraulic machines directly from equipment suppliers. Current manufacturers offering MuCell-equipped machines include Arburg, Battenfeld, Demag Ergotech, Dongshin, Engel, Husky, Italtech, JSW, Krauss Maffei, Milacron, Mitsubishi, Nissei, Toyo, Toshiba, and Van Dorn. All MuCell injection molding machines can operate in the MuCell and conventional modes. Each new or upgraded MuCell injection molding machine has Automated Delivery Pressure Control (ADPC), which has established MuCell as a robust process able to run anywhere in the world with minimal special training, operator involvement, or supervision on a 24/7 schedule. The ADPC is an integrated hardware and software system that automates, controls, and monitors the delivery of SCF into the barrel of the injection molding machine. By continually adapting to normal changes in the injection molding process., the ADPC minimizes the amount of operator expertise required to set up and maintain a consistent MuCell process.

3 The Series II SCF Delivery System pictured in Figure 3 provides a logic controller that can manage the MuCell mechanical properties and dimensional stability under extreme soldering and /or environmental temperatures. functions of the injection molding machine independently of the molding machine controller. FIGURE 3 The Trexel Series SII SCF Delivery System Materials manufacturers have verified the for most semicrystalline thermoplastics including PBT, SPS/PA, PA 66 and HTNs, significantly lower mold temperatures can be used with the MuCell process without a loss in percent crystallinity. This opens opportunities for very substantial cycle time reductions using the MuCell process. FIGURE 5 MuCell Harness Connector Housings Average Cycle Time Reduction: 2% to 3% 3 STRATEGIC MUCELL BENEFITS IN ELECTRONIC CONNECTION SYSTEMS MuCell Strategic Benefit: Cycle Time Reduction Cycle time reductions ranging from 15% to 5% are the result of: 1) The elimination of pack and hold time with internal gas pressure providing the necessary filling pressure. 2) The ability to use significantly lower mold temperatures while maintaining maximum crystallinity levels. FIGURE 4 Sources of MuCell Cycle Time Reduction Start of Injection Hold Cooling Figures 6 and 7 provide DSC curves generated by Ticona GmbH for a conventionally molded and MuCell molded 3% glass fiber reinforced PBT. The conventional samples were molded using an 8ºC mold temperature and the MuCell samples were molded using a 3ºC mold temperature. The curves are nearly identical, confirming that maximum crystallinity was maintained with MuCell while reducing the mold temperature by 6%. FIGURE 6 DSC Curve of Conventionally Molded PBT GF3 with 8 C Mold Temperature (Source : Ticona GmbH) Hold Cooling Melting Temperature: Heat of Fusion ( H): 225, C 41,93 J/g Hold & Pack Eliminated Cooling Time Reduction During conventional molding of electronic connectors, mold temperatures are often elevated to achieve the high crystallinity levels needed to maintain satisfactory

4 processing window for MuCell compared to conventional molding. FIGURE 7 DSC Curve of MuCell Molded PBT GF3 with 3 C Mold Temperature (Source: Ticona GmbH) Melting Temperature: 225, C Heat of Fusion ( H): 41,93 J/g FIGURE 9: MuCell Wiring Harness Connector Housings: Average Cycle Time Reduction: 2% to 25% MuCell Strategic Benefit: Faster Product Release In conventional molding, the process is established such that part weight is a predictor of correct part dimensions. Also in conventional molding, part dimensions are influenced by factors such as variations in mold temperature, variations in wall thickness, and residual stress. Since changes in part weight can cause residual stress in conventional molding, changes in part weight can cause desirable or undesirable changes in part dimensions. Hence, in conventional molding part weight and part dimensions are directly correlated. In contrast, MuCell molding removes residual stress through the elimination of pack and hold pressure. As a result, in MuCell molding part weight and part dimensions are independent. Figure 8 shows this exceptional MuCell dimensional repeatability for 4 part dimensions molded at different conditions to achieve 5%, 1%, and 14% density reductions. MuCell part dimensions are clearly shown to be independent of part weight and this serves as evidence of the wider FIGURE 8 MuCell Part Dimensions are Independent of Part Weight The uncoupling of part weight and part dimensions using the MuCell process provides a wider process window and allows for optimization of the molding process without negatively impacting part dimensions. The Connector Shroud illustrated in Figure 9 was molded conventionally and in MuCell at weight reductions ranging from 3.9% to 1.8%. As expected, no change in gate end and vent end dimensions are observed when changing MuCell process parameters to achieve different part weight reductions. MuCell s superior conformance to the mold cavity is also confirmed through these measurements with an average.2-mm deviation at Dimension 2 in MuCell compared to a.11-mm deviation in conventional molding. FIGURE 9 MuCell Connector Shroud: Uniform Cavity Pressure & Improved Filling Result in More Precise PinHole Positioning Gate End Dim 1 Weight Dim 1 Dim 2 Reduction Mean (Spec) % Solid % MuCell Run 1 3.9% MuCell Run 2 7.1% MuCell Run 3 1.3% MuCell Run 4 8.7% MuCell Run 5 1.8% Vent End Dim 2 The MuCell versus Solid dimensional comparison in Figure 1 highlights the ability to eliminate time-consuming and costly FIGURE 1 Faster Product Release Distance, mm Dim 1 Dim 2 Dim 3 Dim 4 5% 1% 14%

5 Overall Width- Rectangular Box 96.2 Width- Open side Solid Cavity 1 Solid Cavity MuCell Cavities 1 and Position 4 5 (Gate at # 4) Cav1- Solid Cav1- MuCell Cav2- Solid Cav2MuCell tooling iterations with the MuCell process. On the vertical axis is a width dimension with a specification of 96. mm. Each data point represents a different width measurement taken at a different location across the same wall. Using parts from a 2-cavity mold, MuCell and Solid measurements are compared. As expected, the MuCell dimensions are consistent at 95.8 mm across the entire wall width and so the mold adjustment, if necessary at all, will be straightforward. In comparison, Solid Cavity 1 dimensions across the same wall are both above the specification and below the specification due to molded-in stress. This dimensional influence of residual stress complicates the mold modification process enormously, making it difficult to determine with any reasonable degree of certainty the direction of the mold adjustment and order of magnitude of the mold adjustment. In conventional molding, a long struggle to meet the print dimensions for this part may lie ahead. More consistent and predictable MuCell dimensions, through the elimination of molded-in stress, simplify mold design and reduce the number of costly iterations. FIGURE 11 MuCell Traction Control Connector Housing 75% Reduction in Side Wall Bow Material: 15% GF-Reinforced PBT (Source: JSW) A thermoplastic material that has been excluded from a specific connector application because of insufficient flow FIGURE 12 MuCell Viscosity Reduction No rm.8 aliz e.6 Vis cos ity.4.2 Questra PBT PA Solid MuCell with SCF Nitrogen MuCell with SCF Carbon Dioxide length may exhibit sufficient filling, given the marked viscosity reduction that occurs, using the MuCell process. Due to the downsizing of electronic connector designs, material selection is being dictated more frequently by the ability of the polymer to completely fill the part. Material selection driven by flowability can have adverse cost and performance tradeoffs. The inherent viscosity reduction of the MuCell process opens the selection window and enables the adoption of the lowest cost material that is functionally qualified for the application. The bar chart in Figure 12 provides the normalized viscosity of three 3% glass fiber reinforced electronic connector insulator materials (Questra NWA, PBT, and Nylon 66) for conventional molding, MuCell with SCF of nitrogen, and MuCell with SCF of carbon dioxide. The maximum MuCell viscosity reductions are 3% for Questra NWA and 22% for PBT and Nylon 66. MuCell Strategic Benefit: Lower Cost Material Substitution Combined with other MuCell process benefits including the elimination of pack and hold and the lower and more evenly distributed cavity pressures, this viscosity reduction benefit

6 opens substantial cost savings opportunities through lower cost material substitution in electronic connectors. The substitution of conventionally molded LCPs with MuCell molded High Temperature Nylons is one example. Figure 13 shows a glass fiber reinforced PBT connector body that could not be filled at the vent end when molded conventionally using a reduced mold temperature. Using the same mold temperature, complete filling of the connector body was achieved with MuCell. FIGURE 13 Improved Flow. Conventional Molding: Incomplete Filling CONNECTOR PERFORMANCE MuCell: Complete Filling MuCell automotive connectors, including those for sealed under-the-hood systems, have been validated according to the SAE/USCAR-2 performance standard for automotive electrical connector systems. For computer, consumer, and communication electronics, all UL recognized component plastics are also recognized by UL using the MuCell process at up to 5% density reductions (UL746D is the Underwriters Laboratories Standard for Polymeric Materials Fabricated Products). Figure 14 presents.64 mm and 1.5 mm terminal retention force results for a MuCell automotive connector. The minimum and average retention force values exceed FIGURE 14 MuCell Terminal Retention Force (No TPA) SAE/USCAR-2 Rev. 3, Section Material: Glass Fiber Reinforced SPS/PA Newtons mm Terminal 1.5 mm Terminal USCAR Specification Minimum Average USCAR performance standards by a substantial margin. These excellent results are typical for MuCell automotive connectors molded Nylon, HTN, SPS/PA, and PBT Figure 15 provides a comparison of 2.8-mm terminal retention force in MuCell and in Solid for as molded and conditioned connector samples after 4 hours at 4ºC in 98% relative humidity. The chart confirms that the affect of conditioning on conventionally molded and MuCell connectors is the same. FIGURE mm Terminal Retention Force: MuCell vs Solid As Molded & Conditioned (4ºC, 98% RH, 6 hr.) Newtons Breaking Strength - Lbs (4 x 1 mm) FR5 - Tensile - 21 Deg.C Aging Hours Figure 16 presents comparative terminal retention force data after wave soldering for an automotive 129-position ECM FIGURE 16 ECM Header Terminal Retention Force after Wave 26ºC Specification: 24.5 N As Molded Average Pin Retention Force (N) Solid Minimum Pin Retention Force (N) MuCell (1% wt. red.) Solid MuCell Conditioned USCAR S ifi ti header molded in glass fiber reinforced PBT in both MuCell and Solid. The MuCell header achieved higher average and minimum terminal retention forces compared to the conventionally molded header. In this case, MuCell s higher terminal retention force can be attributed to lower residual Solid MuCell

7 stress levels resulting in superior dimensional stability of the thin pin-hole wall sections. Figure 17 summarizes the results of mechanical, electrical, and flammability testing and long-term thermal aging performed by Underwriters Laboratories for a glass fiber reinforced Nylon 66 molded conventionally and in MuCell at 11.9% weight reduction. This data confirms that up to an 11% weight reduction for glass reinforced polyamides molded in MuCell, flammability properties are unaffected and there is no meaningful change in heat distortion temperature and dielectric properties. Furthermore, the data verifies that there is no meaningful difference in mechanical and dielectric property retention under long-term, extreme heat exposure between the MuCell Solid samples. FIGURE 17 MuCell Long-Term Thermal Aging (UL746B) & Mechanical, Electrical, and Flammability Properties Material: Zytel FR5 Source: Underwriters Laboratories Source: Underwriters Laboratories FR5 Dielectric Strength - 19 Deg.C 5 Zytel FR-5 Solid Zytel FR5 MuCell (1% Weight Reduction) Difference Density (g/cc) % UL 94 (.75 mm) V- V- NC UL 94 (3. mm) V- V- NC Tensile Strength, Mpa % Charpy Impact (J/m) % HDT (.45 mm) Degrees, C % HDT (1.8 mm) Degrees, C % Dielectric 5% RH, kv/mm % Dielectric 9% RH, kv/mm % CTI, V NC RTI, Electrical, Degrees, C NC RTI, Tensile, Degrees, C NC RTI, Impact, Degrees, C % THE MUCELL ECONOMIC ADVANTAGE IN ELECTRONIC CONNECTION SYSEMS The hardware and licensing investment associated with implementation of the MuCell Injection Molding Process for electronic connectors yields an average return of 3% to 4% with a Payback Period of 12 to 18 months. Including the hardware amortization and licensing cost per part, the cost savings achieved from deployment of the MuCell process in connector applications averages 12% to 2%. Two examples, an automotive electronic control module header and DIMM socket were selected to show (1) the return and the payback period on a capital investment in the MuCell process (2) the impact of the MuCell process on component cost structure. MuCell Implementation: ECM Header Body MuCell implementation of an electronic control module header body, molded with a glass fiber reinforced HTN in a 2-cavity mold with annual production of 1.1 million units, yields a cost savings of 15.3% (net of amortization and license costs). MuCell process benefits for the header body including 25% cycle time reduction and 5% clamp tonnage reduction are summarized in Figure 18: FIGURE 18 MuCell Process Benefits: ECM Header Body Cycle Time Reduction 25% Clamp Tonnage Reduction 5% Weight Reduction 1% Flatness Improvement 36% Dielestric Str.- KV FR5 Charpy Impact (21 Deg.C) Aging Hours Solid Foamed The MuCell equipment investment, including the MuCell Modular Upgrade of a 15-ton injection molding machine was $97,55. FIGURE 19 MuCell ECM Header Body Charpy Impact - Joules/m Solid Foamed The resulting MuCell financial performance is summarized below: Aging Hours

8 FIGURE 2 MuCell Financial Performance ECM Header Body Implementation First Year Operating Savings $ 15,375 4-Year Program Savings $ 411,5 Net Part Savings Solid Part Cost MuCell Part Cost 15.3% $.542 $.459 Annual Production Hours Saved 1,7 hr Payback Period 1.2 yr. Return on Investment (i=1%) 382% The economic value of 1,7 hr. of machine time saved, (realized in terms of incremental profit from additional parts produced and/or in terms of a capital expenditure avoided for the purchase of an additional machine) has not been incorporated into the financial analysis summarized in Figure 2 but would ordinarily be accounted for in a corporate capital expenditure justification. MuCell Implementation: DIMM Socket MuCell implementation of a DIMM socket product series, with annual production of 3 million units, allowed the socket to be molded using a glass fiber reinforced, High Temperature Nylon in lieu of a more expensive LCP resulting in a cost savings in excess of 4% (net of amortization and license costs). Net Part Savings Solid Part Cost (LCP) MuCell Part Cost (HTN) 44.3% $.114 $.64 Annual Production Hours Saved 573 Annual Program Production Hours 1,719 Payback Period.79 yr. Return on Investment (i=1%) 517% In this case, the MuCell investment has been shown to be profitable using only 1,719 annual productions hours or 3% of the available MuCell injection molding machine capacity. CONCLUSION Deployment of the MuCell process by connector manufacturers is lowering the cost structure of electronic connection systems and reducing the time and expense to develop and launch new products. MuCell technology s superior dimensional conformance to the mold, lower and more uniform cavity pressure, and elimination of residual stress combine to provide a wider processing window than in conventional molding. This results in the ability to optimize the MuCell process faster and to reach print dimensions faster with fewer costly mold modifications. FIGURE 21 MuCell Process Benefits: DIMM Socket Cycle Time Reduction 25% Viscosity Reduction of HTN 22% Weight Reduction 5% The MuCell equipment investment, including the MuCell Modular Upgrade of a 75-ton injection molding machine, was $89,85. The resulting MuCell financial performance is summarized in Figure 22 below: FIGURE 22 MuCell Financial Performance DIMM Socket Implementation First Year Operating Savings $ 17,965 4-Year Product Series Savings $ 683,86 Through reductions in operating costs, material costs, and capital cost avoidance, an investment in MuCell technology for electronic connection systems generates an average return of 3% to 4% and average cost savings of 12% to 2% with a payback period below 18 months. With the exceptional functional performance of MuCell connector components now proven in the harshest environments through validations such as SAE/USCAR-2, MuCell processing is being viewed in the boardrooms of leading connector manufacturers as a mainstream technology that yields a unique and powerful financial advantage and reduces time to market. The nitrogen or carbon dioxide SCF used in the MuCell process acts as a temporary plasticizer, reducing melt viscosity up to 3%. Lower cost material options such as the replacement of LCPs with flow-limited High Temperature Nylons via MuCell implementation represent an strategic cost savings opportunity for connector manufacturers.

9 The ability to add MuCell capability to almost any existing injection molding machine through the MuCell Modular Upgrade means that connector manufacturers can (1) deploy the MuCell process quickly while utilizing idle or unproductive machine capacity and (2) avoid new machine purchases through the resulting cycle time reductions that average 2% to 3%. Across the spectrum of electronic connection systems, from board level connectors to automotive wiring harness connectors, three strategic benefits; (1) cycle time reduction, (2) faster product release, and (3) lower cost material options will continue to propel MuCell deployment around the world.. Questra is a registered trademark of Dow Chemical Zytel is a registered trademark of DuPont REFERENCES 1 Ticona GmbH, MuCell Technology, October Ticona GmbH, MuCell Microcellular Foam Molding, October 1, 21 CONTACTS The authors can be contacted as follows: LEE J. HYDE Business Director Trexel, Inc. 45 Sixth Road 45 Sixth Road Woburn, MA 181 Woburn, MA 181 LEVI A. KISHBAUGH Vice President, Engineering Trexel, Inc. Tel (781) Tel. (781) l.hyde@trexel.com l.kishbaugh@trexel.com